1. Field of the Invention
This invention relates to a mirror device adjusted to 90 degrees, for example, for use in a slit exposure optical system of an electrophotographic copying machine or the like. More specifically, the present invention relates to a mirror device having a mirror support and an adjusting device for adjusting the mirror support with respect to an optical path.
In an electrophotographic copying machine or the like, a mirror assembly adjusted to 90 degrees, for example, has been employed in order to convert the optical path ranging from an exposing portion to a photosensitive member of an image-reproducing portion and to keep constant the optical path length.
In a support of 90.degree.-mirrors, alignment characteristics of two mirrors orthogonal to each other exert significant influences upon focus, distortion, and extension and diminishment of an image, and the like. For this reason, it is a customary practice to cast a block as the base of the assembly by die-casting or the like and to cut out a reference surface for locating the mirrors on this block by precision mechanical cutting work or to provide an adjusting screw to the base that has been subjected to bend working. Accordingly, in the former construction, the weight of the 90.degree.-mirror support becomes great so that a load for moving the mirrors at the time of exposure for copying becomes great and large inpact is applied to the support when the mirrors stop. Moreover, this construction results in the increase in the cost of production. In accordance with the latter construction, on the other hand, strength of the assembly is likely to become insufficient so that the adjusting screw accidentally gets loose, thereby causing various problems.
In the 90.degree.-mirror support of the abovementioned kind, it is necessary to secure the three-dimensional position and posture of the exposure optical system relative to the optical axis. Accordingly, conventional 90.degree.-mirror supports are equipped with a built-in fine adjusting mechanism for performing the fine adjustment of the mirror positions and angles. When this adjusting mechanism is employed, however, the 90.degree.-mirror support inevitably becomes complicated in construction and great in weight so that the cost of production of the product increases and the allowance for adjustment is restricted. To cope with this problem, accuracy of finishing and assembly must be made severer for other constituents.